Picture a polar bear stalking an unsuspecting walrus in the frozen Arctic: The predator slowly inches closer, camouflaged by ice and snow, until it's close enough to pounce. And then it delivers the killing blow — by bopping the walrus on the head with a large rock.
That might sound like something you'd see in a cartoon, rather than in nature. But for centuries, Inuit people in the Arctic have shared such stories with non-Native explorers and naturalists, describing polar bears killing or stunning prey with stones and chunks of ice that the bears grasp in their paws (or throw off cliffs onto animals at the bottom, according to a memorable 19th-century engraving).
A new study looked at Inuit anecdotes describing this behavior — "from a diversity of locations and over a long period of time" — and found they were so widespread and consistent that they suggested that in rare cases, polar bears likely wield such objects as weapons. However, until scientific researchers actually catch the Arctic bears in the act of bludgeoning walruses, it's hard to say for sure.
"I have always been impressed with the accuracy and reliability of the observations of animals reported by experienced Inuit hunters, so I thought it was likely the accounts might not just be myths but the result of reporting of actual observations, even though the behavior itself is likely quite rare," study lead author Ian Stirling, a member of the Scientific Advisory Council for Polar Bears International and an adjunct professor in the Department of Biological Sciences at the University of Alberta, told Live Science in an email.
Inuit descriptions of polar bears (Ursus maritimus) hoisting — and sometimes hurling — hefty blocks of rock or ice date to the late 1700s, according to the study. In a description that naturalist Otto Fabricius wrote in 1780 in the book "Fauna Groenlandica," polar bears grab sizable ice chunks and launch them at walruses' heads.
"The bear makes it [the walrus] lose its balance (or 'stagger' is more literal) and thus kills it easily," the scientists wrote in the June issue of the journal Arctic.
An Inuit account from 1883 described another ice-chucking bear that "seized a mass of ice in his paws, reared himself on his hind legs, and threw the ice with great force on the head of a half-grown walrus." A 1925 record of another Inuit report noted that a polar bear "carefully selected a young walrus and threw the ice block down upon it with such a force that it became immobilized," the study authors wrote.
In one astonishing example, illustrated by the 19th-century Arctic explorer Charles Francis Hall, a polar bear allegedly threw a boulder onto a walrus's head from atop a tall cliff. Hall published an engraving of the scene in 1865, basing it on a description by his Inuk guide from Baffin Island.
"The bear mounts the cliff, and throws down upon the animal's head a large rock, calculating the distance and the curve with astonishing accuracy, and thus crushing the thick bullet-proof skull," Hall wrote in the book "Arctic researches, and life among the Esquimaux" (Harper & Brothers, 1865).
"If the walrus is not instantly killed — simply stunned — the bear rushes down to the walrus, seizes the rock, and hammers away at the head till the skull is broken," Hall concluded, according to the study.
Tools in captivity
The scientists also reviewed more recent reports, by Inuit and non-Inuit witnesses, that suggested the bears used rocks and ice for hunting and for disabling human hunters' traps. But these conclusions were based on the placement of rocks and ice that the bears had left behind and did not reflect observations of the bears actually using the objects as tools, the scientists wrote.
However, in 2010, photos showed a captive male polar bear named GoGo at the Tennoji Zoological Gardens in Osaka, Japan, using "tools" in his enclosure to reach a piece of food. Caregivers had hung a piece of meat about 10 feet (3 meters) above GoGo's pool — too high for him to grab — "to provide stimulation and distract his attention" by challenging GoGo with solving this puzzle, according to the study.
At first, GoGo tried jumping at the meat. But after a month of failure, he "invented" two tools: a piece of plastic pipe that he chucked at the food, and a branch measuring around 7 feet (2 m) that he used to smack the meat and knock it off its hook. Initially, GoGo took several hours to succeed, but he was soon able to knock down the meat in just 5 minutes, the researchers reported.
GoGo's example, together with centuries of anecdotes and other recent observations, hints that tool use for hunting among wild polar bears — though likely not a common occurrence — is certainly possible, according to the study.
"An occasional adult polar bear might be capable of mentally conceptualizing a similar use of a piece of ice or a stone as a tool," the study authors reported. However, such extreme measures are probably used only for the biggest prey that polar bears hunt: walruses.
Polar bears prey on walruses and seals, but walruses are much more formidable targets. While an adult ringed seal (Pusa hispida) may weigh up to 165 pounds (75 kilograms), a 2-year-old walrus (Odobenus rosmarus) can weigh a whopping 750 pounds (340 kg) and full-grown adults may weigh as much as 2,000 pounds (907 kg), according to the Alaska Department of Fish and Game. What's more, walruses have long tusks to defend themselves during melee encounters, and their skulls are denser and harder to crack than seal skulls, Erica Hill, a professor of anthropology at the University of Alaska Southeast, reported in 2017 in the journal Études/Inuit/Studies. (Hill was not involved in the recent study.)
The targets of occasional boulder hurling by adult polar bears are therefore most likely to be walruses, the researchers concluded.
Originally published on Live Science.
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Mindy Weisberger is an editor at Scholastic and a former Live Science channel editor and senior writer. She has reported on general science, covering climate change, paleontology, biology, and space. Mindy studied film at Columbia University; prior to Live Science she produced, wrote and directed media for the American Museum of Natural History in New York City. Her videos about dinosaurs, astrophysics, biodiversity and evolution appear in museums and science centers worldwide, earning awards such as the CINE Golden Eagle and the Communicator Award of Excellence. Her writing has also appeared in Scientific American, The Washington Post and How It Works Magazine.